1. Field of the Invention
The present invention relates to a recording medium playing apparatus for playing a recording medium such as a video disc or a digital audio disc.
2. Description of Background Information
A system has been proposed in which picture information is recorded and reproduced in the form of the subcode on and from a digital audio disc having a diameter of 12 cm, generally called compact disc (abbreviated as CD hereinafter). The subcode is made up of eight subcode bits, and bit groups forming the subcode are divided into eight channels denoted respectively by letters P, Q, R, S, T, U, V, and W. In the method in which the picture information is recorded and reproduced in the form of the subcode, data corresponding to picture information is configured such that a symbol is formed by 6 bits of channels R through W out of the 8 bits forming the subcode, and 98 symbols are treated as one block, as illustrated in FIG. 1. Two symbols in the 98 symbols are used as a sync signal, and 24 symbols obtained by dividing the remaining 96 symbols, by four are treated as a minimum unit of data, i.e. a "pack", which constitutes one instruction of picture processing.
More specifically, the first symbol (referred to as symbol 0 hereinafter) of the 24 symbols shows one of several modes. A symbol 1 following this symbol 0 forms "instruction" which indicates the sort of the instruction. Symbols 2 and 3 following the symbol 1 constitute a "parity Q" which is an error correction code. Symbols 4 through 19 following the parity Q constitute a data field, and include information such as color information. Finally, symbols 20 through 23 following the data field constitute a parity P which is an error correction code for protecting the information in the "pack".
There are four modes, i.e. "zero mode", "line-graphics mode", "TV-graphics mode", and "user's mode". The "zero mode" is provided for a case where no operation is required for pictures on the display screen, that is, the original image is to be maintained, and all data in the "pack" are 0 for this mode.
The "line-graphics mode" is provided for such a case that a liquid crystal display is provided on the front face of the player, to display notes such as an explanation of a music selection. As shown in FIG. 2, a picture area elongated sideways is formed by pixels which are arranged in 288 columns and 24 rows. In other words, each row includes 288 pixels and each column includes 24 pixels. The term "pixel" stands for the minimum display element of a picture, and it is general that the picture processing is performed by using picture composing units designated as "fonts" each of which is made up of pixels divided into 6 columns and 12 rows.
The number of "fonts" which can be displayed in the "line-graphics mode" is 48 in the lateral direction, and 2 in the column direction, and this area is designated as "screen area". For providing the scroll function, a line of "fonts" is added to the upper and lower outer peripheries and the right and left peripheries of the screen area, to form a picture area having 50 "fonts" in the direction of row, and 4 "fonts" in the direction of column. The subcode is formed so that the picture processing is performed by using a memory having addresses each corresponding to each pixel in this picture area. In addition, the area outside the "screen area" is designated as "border".
The "TV-graphics mode" is a mode for displaying images on the TV screen, and a picture is formed by pixels arranged in 192 rows and 288 columns as illustrated in FIG. 3. The number of "fonts" which can be displayed in the "TV-graphics mode" is 48 in the direction of row, and 16 in the direction of column. Also in this "TV-graphics mode", the subcode is formed so that the picture processing is performed by using a memory having addresses each of which corresponds to each pixel in a picture area having 50 "fonts" in the direction of row, and 18 "fonts" in the direction of column, made by adding a line of "fonts" to the upper and lower peripheries as well as the right and left outer peripheries of the "screen area".
Instructions for the picture processing, include an instruction for painting out the whole picture area with one certain color, an instruction for drawing a picture in one "font" on the screen by using two different colors, an instruction for moving the whole picture upward or sideways, and so on.
Additionally, in the 8-bit groups forming the subcode, the Q bits forming the channel Q include time information corresponding to the track length to a certain position of each information data which is recorded from the beginning of the program area of the CD, and from address time data which can be used as positional data representing the recording position. On the other hand, the P bits forming the channel P form data including information relating to a pause between two music selections.
In the case of the above-described system for recording and reproducing picture information as the subcode, at most nineteen picture channels can be designated. Specifically, a "write font foreground/background" instruction is used in the "TV-graphics mode", which has such a structure as illustrated in FIG. 4. This is an instruction for writing font data of the symbols 8 through 19 in positions having a row address defined by the symbol 6 and a column address defined by the symbol 7. For the pixels whose font data is "0", a color of a color number determined by the "color 0" is designated as a background color. For the pixels whose font data is "1", a color of a color number defined by "color 1" is designated as a foreground color. At the same time, sub-picture channels can be designated by using four bits of the channels R and S of the symbols 4 and 5. By this feature, as many as sixteen picture channels can be designated. Sixteen sorts of pictures are previously recorded on a disc for example, and on the playing side, a desired picture channel can be selected at the time of playback by this scheme of designating the picture channel.
In addition, the sixteen colors indicated by the color number "0" through "15" are set by a "load CLUT color 0 through color 15 (load color look-up table color 0 through color 15)" instruction. The "load CLUT color 0 through color 15" instruction is an instruction having a structure illustrated in FIG. 5, and setting the contents of a color look-up table showing the color of pre-set color numbers or foreground/background color numbers. It is necessary to designate sixteen colors in total. However, since four bits are used respectively for each of RGB to indicate a color, two symbols are required for setting one color. Therefore, eight colors are set by one "pack" at most. With these circumstances, this instruction is divided into two instructions respectively designating eight colors of the first half, and eight colors of the second half.
The instruction code for the colors of the first half, i.e. the color 0 through the color 7, is determined to be "30", and the instruction code for the colors of the second half, i.e. the color 8 through color 15 are determined to be "31". The mixing of colors for each color number is as follows. Red is represented by four bits of the channels R through U of even symbols allotted to the color number. Green is represented by four bits, i.e. two bits of the channels V and W following the channels R through U of the even symbols, and two bits of the channels R and S of odd symbols. Blue is represented by four bits of channels T through W following the channels R and S of the odd symbols. Therefore, 2.sup.4 (=16) sorts of gray scales are available for each color, and preparation of 16.sup.3 (=4096) colors is possible since three colors (RGB) are used. In addition, a gray scale "0000" corresponds to the darkest state, and a gray scale "1111" corresponds to the brightest state.
The applicants of the present application have invented a system for recording on a recording medium an FM modulated video format signal in addition to a digital audio signal to which graphic codes including picture information are inserted according to the above-described system for recording and reproducing picture information as the subcode, so that the image obtained by the subcode can be inserted into the picture obtained by the video format signal at the time of play of the recording medium. The system is disclosed in Japanese Patent Application No. P63-46603.
In order that the picture represented by the FM modulated video format signal and the picture represented by the subcode can be displayed in the same screen at the same time, the system of this prior application uses a new code as illustrated in FIG. 6 to be inserted as the symbol 0 to designate an additional mode, that is, "graphic mode with motion picture" in addition to the "zero mode" the "line-graphics mode", the "TV-graphics mode" and the "user mode" which are also used in the conventional method for recording and reproducing picture information using the subcode.
The structure of a picture in the "graphics mode with motion picture" is identical with that in the "TV-graphics mode", and an instruction designated as "load transparency control table" as illustrated in FIG. 7 is provided. This "load transparency control table" instruction is an instruction for designating the mode for each pixel in picture area. Three modes are designated by this instruction, and those are namely, "transparent mode", "mixing mode", and "non-transparent mode". In these three modes, different values are selected for the mixing ratio between a video format signal obtained by the subcode and a video format signal which is recorded by multiplexing operation together with the coded information signal including the subcode.
The bits in the channels R through W of each of the symbols 4 through 8 and the channels R and S of the symbol 9 constitute a series of codes TCB-0 through TCB 15 which respectively designate one of modes which will be described later for each of the group of pixels to which one of colors, which are registered as color number "0" through color number "15", is allotted. FIG. 8 shows the relationship between bit patterns of the codes TCB-0 through TCB-15 and the modes designating the mixing ratio, and the mixing ratio in each mode.
A recording medium playing apparatus for playing a recording medium on which information is recorded by the system of the prior application described above, is also disclosed in Japanese Patent Application No. P63-46603. This recording medium playing apparatus is constructed such that the picture signal obtained by the subcode and the video format signal recorded in the FM modulation form are mixed and output at a mixing ratio according to the graphic codes representing the color of each pixel in the display area of the image by the subcode.
However, in the system described above, the display position of the image by the subcode is set at the middle position of the display area of the image by the video format signal FM modulated for recording. Therefore, in this recording medium playing apparatus, if the display of caption (superimposed dialogue), for example, is performed by using the subcode, the caption will be displayed in the middle portion of the image by the video format signal, and such state is undesirable since the presence of the caption is annoying to the viewer.